The present invention relates to a composite gasket adapted to be inserted into a groove. In one preferred embodiment, the invention is a gasket adapted to be inserted into the groove of a manway cover and securely held therein without the need for mechanical or adhesive attachments. The composite structure of the gasket including an inert polymer wrapped around a metal insert provides for superior sealing of the gasket over multiple uses.
Manways are built into many constructions for a broad range of uses. Those uses include, but are not limited to, their use on railway tank cars and other large storage tanks that hold chemicals. These tanks are prevalent throughout the chemical processing, waste treatment, pulp and paper and other industries.
Particularly in railcar manway applications, the gaskets that are used, typically installed in the manway cover, are subjected to substantial abuse. The rail workers themselves may treat the manway cover roughly during loading and unloading operations. Also the contents of the tank may slosh around during transport to come in contact with and corrode the gasket. The conventional method for applying a ring gasket to the manway is to secure it within the groove in the manway cover with an interference fit. Also, once installed, the gasket is often ignored until a leak is discovered, so it will be subject to abuse for extended time periods. With an interference fit type of application, the manway gasket is not mechanically secured into the manway cover groove and can fall into the tank car during opening and closing of the manway cover. When a chemically aggressive product is being shipped, it may attack and degrade (or compound other mechanical damage over time) certain types of gasket material causing resulting leakage. Most polymer-type gaskets are not reusable, because they are too soft and permanently deform once initially compressed. Also, while polymer gaskets can maintain an initial seal, creep and rail car vibration can cause a seal to degrade during long term operation. Gasket creep and rail car vibration will cause the fasteners retaining a manway cover to loosen. This results in a loss of gasket stress and eventually a leak. Additionally, as a manway nozzle becomes worn and pitted through use over time, hard polymer based or conventional sheet materials and metal gaskets alone can not fill the worn and pitted surface to effect a seal.
In the case of railcar manways, updated inspection procedures sometimes require a pressure test of the sealed railcar, so gasket performance has become more demanding. Still further, increased inspections for and fines related to non-accidental releases (leaks) from a railcar has also focused attention on railcar manway gasketing reliance and durability.
Many solutions have been tried to cure the gasket problems noted herein. Soft polymers that make a good seal are not effectively reusable and may fall out of the groove when the manway is open. Durable polymers that are inert to chemicals may be too soft or may have the same problems of soft polymer gaskets only in that they become loose or can crack or distort. Metal gaskets alone are subject to corrosion and are also not stretchable like a polymer, so it can be difficult to install a metal gasket in a groove and keep it there. Composite gaskets have been attempted where a polymer layer is adhered to the face of a metal gasket. A problem with this layer construction occurs when a corrosive material that may be carried in the tank car may attack the adhesive holding the gasket together. Impurity in the tank results as the adhesive may mix with and contaminate the tank contents. Also, the polymer layer may peel off and fall into the tank when the cover is opened if the adhesive is weakened or dissolved. A still further alternative solution was a composite gasket mounted on the manway nozzle (the male edge that is received in the manway cover groove). Despite an effective sandwich construction where the metal portion of that gasket had inert polymer material wrapped around it, these nozzle gaskets were too exposed to physical abuse. The cleaning and filling functions of the rail car are accessed through the manway. Inevitably, there was physical damage to the gasket that prevented it from effectively and reliably being reusable on a consistent basis.
Accordingly, it is an object of the present invention to overcome the foregoing drawbacks and to provide a durable gasket adapted to be inserted into a manway cover groove. The present invention is a composite gasket that delivers the benefits of both a polymer gasket (inertness), an elastomer gasket (reuse-ability, low bolt load), and a metal gasket (durability, secure containment in groove) while at the same time being protected from potentially corrosive effects of the tank contents.
In one embodiment, a manway cover gasket is adapted to be mounted into a groove in a manway cover. The groove comprises an inside diameter. The gasket comprises an annular rigid insert having a top surface and bottom surface, and an inside edge and an outside edge and corresponding inside and outside diameters. A polymer strip is wrapped around and substantially covers the top and bottom surfaces of the rigid insert. The polymer strip comprises an overlap portion inside the inside diameter of the rigid insert, this overlap defining an inside diameter of the gasket. The inside diameter of the rigid insert is no less than substantially the same as the inside diameter of the manway cover groove, and the inside diameter of the gasket is less than the inside diameter of the rigid insert. The rigid insert may be comprised of stainless steel, and it may be corrugated. The rigid insert may also comprise tabs that extend radially outwardly from the outside diameter of the rigid insert or radially inwardly from the inside diameter of the rigid insert. The polymer strip may be comprised of expanded PTFE. The manway cover groove defines an opening width between the groove inside diameter and groove outside diameter. The opening width of the groove is then less than the width of the groove inside the opening. Further, the width of the gasket may be greater than the opening width of the groove.
In a still further embodiment, a manway cover gasket is adapted to be mounted within a groove in a manway cover. The groove comprises an inside diameter. The gasket comprises an annular rigid insert having a top surface and a bottom surface and an inside edge and outside edge and corresponding inside and outside diameters. Two annular strips of polymer having an inside and an outside diameter are adhered, one on each side, to the rigid insert. The annular strips of polymer substantially cover the top and bottom surfaces of the rigid insert. The inside diameters of the polymer strips are less than the inside diameter of the rigid insert. An overlap portion is formed from the portion of the polymer strips inside the inside diameter of the rigid insert. The inside diameter of the rigid insert is no less than substantially the same as the inside diameter of the manway cover groove. The rigid insert may be comprised of stainless steel and it may be corrugated. The rigid insert may comprise tabs that extend radially outwardly from the outside diameter or radially inwardly from the inside diameter of the rigid insert. The polymer strips may be comprised of expanded PTFE. Further alternatively, the manway cover groove may define an opening width between the groove inside diameter and outside diameter, and the opening width of the groove is less than the width of the groove inside the opening. The width of the gasket may then be greater than the opening width of the groove.
In another embodiment, a manway cover gasket is adapted to be mounted into a groove in a manway cover. The groove comprises an outside diameter. The gasket comprises an annular rigid insert having a top surface and bottom surface, and an inside edge and an outside edge and corresponding inside and outside diameters. A polymer strip is wrapped around and substantially covers the top and bottom surfaces of the rigid insert. The polymer strip comprises an overlap portion outside the outside diameter of the rigid insert wherein the polymer strip defines an outside diameter of the gasket. Further, the outside diameter of the rigid insert is no more than substantially the same as the outside diameter of the manway cover groove, and the outside diameter of the gasket is greater than the outside diameter of the rigid insert.